Positive impact of 1,25-dihydroxy vitamin D3 on vitamin D receptor and renal fibrosis in diabetic nephropathy rats

Objective To determine the role and possible mechanisms of 1,25-dihydroxy vitamin D3 and vitamin D receptor (VDR) in anti-fibrosis of diabetic nephropathy (DN). Methods DN rats (n=24) were randomly divided into 4 groups as blow: (1) over-expression with arachis oil group (group A, n=6); (2) over-expression with vitamin D group (group D, n=6); (3) virus vector with arachis oil group (group B,n=6); (4) virus vector with vitamin D group (group E, n=6). Six normal rats was resigned as control group with arachis oil (group C, n=6). DN rats were injected different lentivirus with transforming growth factor beta 1 (TGF-β1) to establish the model. After a 37 days gavage of 1,25-dihydroxy vitamin D3 or arachis oil, the kidney was taken out as samples. The structure and morphology change in kidney tissues was observed by electron microscope and Masson staining; the expressions of mRNA and protein of TGF-β1, VDR, moynocte chemoattractant protein-1 (MCP-1), collagen-1 (Col-1) in kidney tissues were measured by immunohistochemistry, Western blotting and real-time PCR. Variance analysis was used to compare among multigroups, and t test was used to compare two groups. Result (1) Glomerular fibrosis was correlated with TGF-β1 level. (2) MCP-1, Col-1 mRNA and protein expressions were all decreased (all P<0.05), while VDR was increased in group A (0.65±0.44, 2.01±0.70), B (1.17±0.59, 3.19±1.01) and C (3.93±1.17, 5.38±0.48) with the reducing level of TGF-β1 (F=19.28, 19.11, all P<0.01). (3) After the intervention of 1,25-dihydroxy vitamin D3 in group D, TGF-β1, MCP-1 and Col-1 mRNA and protein expressions are decreased (all P< 0.05); while VDR mRNA and protein expressions was increased (t=5.61, 2.95; all P<0.05), compared with group A. In group E, TGF-β1, MCP-1 and Col-1 expressions were decreased (all P<0.05); while VDR was increased (t=5.42, 3.33; all P<0.05), compared with group B. (4) The severity of renal fibrosis is improved after vitamin D treatment in electron microscope, Masson staining. Conclusion 1,25-dihydroxy vitamin D3 may have anti-fibrosis effects in DN by down-regulating the expression of renal fibrosis factors, such as TGF-β1, MCP- 1 and Col- 1, and increasing the expression of VDR. Under different expression of TGF-β1 in kidney, 1,25-dihydroxy vitamin D3 may also plays a protective role in diabetic nephropathy via the pathway above. Key words: Calcitriol; Diabetic nephropathy; Transforming growth factor beta 1; Vitamin D receptor